Add support for CDC (Change events)

[jamessimone]

Giving people more options for invoking Rollup: https://trailhead.salesforce.com/en/content/learn/modules/change-data-capture/subscribe-to-change-events-using-an-apex-trigger

[jamessimone]

Started the re-work to include CDC support in v1.0.4 - forthcoming. Because CDC is async, there are some irregularities with the way data comes into Rollup that need to be considered:

• Trigger.operationType is always AFTER_INSERT (requires re-working how the Trigger context is assigned to fit with CDC's model for updates, which comes from the changeType property on the ChangeEventHeader object)
• Reparenting. This is a big one. CDC events come with a list of changed fields, and you would know based on the type of rollup being performed if the lookup field on the calc item had changed - but because the lookup/key field on the calc item would have already been changed (and because CDC does not include the prior field values in what gets sent), figuring out how to perform a recalculation on the old parent record is … difficult

I've made good progress on basic support for CDC and expect that to be released in the coming days, without tackling the reparenting issue highlighted above.